On PRS-300, it looks like there are lot of claws & adhesive sheets while opening up the reader. I am not sure whether this is hard or not. Whereas on PRS-505, there are only couple of screws.

On 300, battery part is called "battery assy", whereas on 505 its called "(ion) storage battery assy".

Yes, doknek. I have opened it to remove the battery because the battery is dead. Opening the device is not very difficult. Surprising there are no replacement batteries available anywhere when the device has been out for over a year and a half. The PRS-505 battery looks slightly bigger from the photographs and is 750 mAh while the PRS-300 battery is only 600 mAh.

At the moment I have plenty of books available of the dead tree variety, so I'd rather wait for the batteries to arrive on the market than try to fit the bigger battery in by removing the metal housing.